MANUFACTURABLE CoWP METAL CAP PROCESS FOR COPPER INTERCONNECTS

ABSTRACT

A method to electrolessly plate a CoWP alloy on copper in a reproducible manner that is effective for a manufacturable process. In the method, a seed layer of palladium (Pd) is deposited on the copper by an aqueous seeding solution of palladium acetate, acetic acid and chloride. Thereafter, a complexing solution is applied to remove any Pd ions which are adsorbed on surfaces other than the copper. Finally, a plating solution of cobalt (Co), tungsten (W) and phosphorous (P) is applied to the copper so as to deposit a layer of CoWP on the Pd seed and copper.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of acobalt/tungsten/phosphorus (CoWP) metal cap for a copper interconnectand, more particularly relates to a manufacturable process for theformation of the CoWP metal cap on such copper interconnect.

Metallization patterns on integrated circuits can be formed bydepositing a dielectric layer, patterning the dielectric layer to form atrench and then depositing a metal layer that fills the trench in thedielectric layer. The metal layer typically not only fills the trenchesbut also covers the entire semiconductor wafer. Therefore, the excessmetal is removed using either chemical-mechanical polishing (CMP) or anetchback process so that only the metal in the trenches remains.

As wire widths in integrated circuits continue to shrink, the electricalconductivity of the wiring material becomes increasingly more important.The material of choice, aluminum, is becoming less attractive than othermaterials, such as copper, which are better conductors. In addition topossessing superior electrical conductivity, copper is more resistantthan aluminum to electromigration, a property that increases inimportantance as wire cross-sectional areas decrease and applied currentdensities increase. Copper is seen as an attractive replacement foraluminum because copper offers low cost, ease of processing, lowersusceptibility to electromigration, and lower resistivity.

Copper has several serious disadvantages as a wiring material. It candiffuse rapidly into and through silicon substrates and dielectricfilms, such as silicon dioxide. Diffusion into an adjacent dielectricregion can cause formation of a conductive path between two interconnectlines producing an electrical short. Diffusion into an adjacent siliconsubstrate can cause junction leakage, thereby destroying the device.Copper also has poor adhesion to the dielectric capping layer.Replacement of aluminum with copper as an interconnect material requiresthat these problems be overcome.

To alleviate the problem of copper adhering to the overlying dielectriccapping layer, various metal caps have been proposed to cap the copperinterconnect so as to increase adhesion to the overlying dielectriccapping layer. One such proposed metal capping material is CoWP. Dubinet al. U.S. Pat. No. 5,695,810, Edelstein et al. U.S. Pat. No. 6,153,935and Sambucetti et al. U.S. Patent 6,323,1 28, the disclosures of whichare incorporated by reference herein, all disclose the electrolessdeposition of CoWP. In Dubin et al., electrolessly plated CoWP is usedas a barrier layer between the copper and the dielectric. Dubin et al.further discloses that a palladium (Pd) seed is sputtered on thedielectric for adhesion of the CoWP but no seed is deposited on thecopper when the CoWP is used as a metal cap.

In Edelstein et al., a Pd seed is formed on the copper wiring materialby a Pd solution of undisclosed composition prior to electrolessdeposition of the CoWP. Residual Pd seed (not adhered to the copper) isremoved by an aqueous solution of a strong complexing agent such asethylenediamine, citrate, or ethylenediamine tetraacetic acid.

In Sambucetti et al., copper wiring material is pretreated with H₂SO₄followed by treatment with a Pd solution of undisclosed composition tocause deposition of a Pd seed followed by a solution containing at least15 g/l of sodium citrate or ethylenediamine tetraacetic acid to removeexcess Pd ions. The copper wiring material is then electrolessly platedwith CoWP.

Babu et al. U.S. Pat. No. 4,956,197, the disclosure of which isincorporated by reference herein, discloses the electroless plating ofnickel or copper onto a dielectric substrate. The dielectric substrateis pretreated with an NH₃ plasma followed by treatment with a PdCl₂seeding solution containing HCl. The PdCl₂ is an extremely aggressiveseeding solution and is unacceptable for the copper interconnects of thepresent invention.

Akai et al. U.S. Pat. No. 4,622,069, the disclosure of which isincorporated by reference herein, discloses the electroless plating ofnickel or copper onto a ceramic substrate. Prior to electroless plating,the ceramic substrate was treated with an organic Pd seed solution todeposit a Pd seed.

Notwithstanding the efforts of those skilled in the art, there remains aneed for a manufacturable process for depositing a CoWP capping layerfor a copper interconnect.

Accordingly, it is an object of the present invention to have a processfor depositing a CoWP capping layer for a copper interconnect which iswell-controlled and repeatable.

It is another object of the present invention to have a process fordepositing a CoWP capping layer for a copper interconnect using a Pdseed solution which enables robust seeding for CoWP while minimizingchemical attack of the copper interconnect.

These and other objects of the invention will become more apparent afterreferring to the following description of the invention.

BRIEF SUMMARY OF THE INVENTION

The objects of the invention have been achieved by providing, accordingto a first aspect of the invention a method of electrolessly plating oncopper contained in or on a substrate comprising the steps of:

applying to the substrate an aqueous seeding solution of palladiumacetate, acetic acid, and a chloride so as to form a palladium seedlayer on the copper only and not on the remainder of the substrate;

applying to the substrate a complexing solution to remove palladium ionsadsorbed on the substrate; and

electrolessly plating the copper with a plating solution comprisingcobalt, tungsten and phosporus so as to deposit a layer of cobalt,tungsten and phosphorus on the palladium seed.

According to a second aspect of the invention, there is provided amethod of depositing a seed layer on copper comprising the step of:

applying to the copper an aqueous solution of palladium acetate, aceticacid, and a chloride so as to form a palladium seed layer on the copperonly.

According to a third aspect of the invention, there is provided a methodof electrolessly plating on copper contained in or on a semiconductorwafer comprising the steps of:

providing a semiconductor wafer having copper areas and non-copperareas;

applying to the semiconductor wafer an aqueous solution of palladiumacetate, acetic acid, and a chloride so as to form a palladium seedlayer on the copper areas only and not on the non-copper areas;

applying to the semiconductor wafer a complexing solution to removepalladium ions adsorbed on the non-copper areas; and

electrolessly plating the copper with a plating solution comprisingcobalt, tungsten and phosporus so as to deposit a layer of cobalt,tungsten and phosphorus on the palladium seed.

According to a fourth aspect of the invention, there is provided aseeding solution for depositing a palladium seed on copper comprising anaqueous solution of palladium acetate, acetate and chloride.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The Figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a schematical representation of a copper interconnectillustrating a preferred embodiment of the present invention.

FIG. 2 is a graph illustrating the efficacy of a gas filter to filtercolloidal particles from the seeding bath.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures in more detail, and particularly referring toFIG. 1, there is shown an article 10 which is exemplary of a preferredembodiment of the present invention. The article 10 comprises asubstrate 12, preferably a semiconductor substrate and, most preferably,a semiconductor wafer. The semiconductor wafer can be made of anysemiconductor material such as silicon, silicon germanium or galliumarsenide, just to name a few. The substrate 12 may have electricalcircuitry and other features which are not germane to the presentinvention. Over the substrate 12 is formed a layer 14 which ispreferably an insulating layer and, most preferably, is a dielectriclayer such as an oxide (e.g., silicon dioxide). Within layer 14 isformed a trench 16 which holds the copper 20. If the article 10 is usedfor electronic applications, it may be necessary to form a liner 18between the copper 20 and layer (e.g., dielectric) 14. The liner isconventional and may be formed of a CoWP alloy but more usually isformed of a bilayer of TaN (tantalum nitride) and Ta (tantalum). Lastly,the article 10 comprises a layer of CoWP 22 which has been electrolesslyplated on the copper 20. Not shown in FIG. 1 is the Pd which isconventionally used to “seed” the copper so that the CoWP can beeffectively and uniformly deposited. If there is a liner, the linertypically will not be seeded or plated.

Others have proposed Pd seeding as a precursor to the electrolessplating of CoWP. However, the prior art solutions proposed by othershave been found to be unsuitable for use in manufacturing where arepeatable process is absolutely necessary. This is particularly thecase in the electronics industry where the copper wiring is very small(on the order of 90 nm in current state of the art semiconductormanufacturing).

The present inventors have set forth an electroless plating processwhich is less aggressive towards the copper and minimizes colloids whichcan cause stray plating of the CoWP on non-copper surfaces.

According to the present invention, there is disclosed a process forelectrolessly plating on copper that is contained in or on a substrate.That is, the copper may be in a trench, as shown in FIG. 1, or may besimply on the surface of a substrate. In the most preferred embodimentof the present invention, the substrate is a semiconductor wafer.

In the first step of the inventive process, the copper surface may beoptionally precleaned to remove any residues from previous processingoperations. For example, when the substrate is a semiconductor wafer, itmay have undergone chemical-mechanical polishing which leaves apassivating layer of BTA (benzotriazole). In this case, it may bedesirable to preclean the copper to remove the BTA or other residue. Twoprecleaning subprocesses have been proposed by the present inventors. Inthe first precleaning subprocess, the article 10 is heated to 100° C. innitrogen for a predetermined period of time (e.g., 30 to 120 minutes)followed by application of an oxalic acid solution, preferably 5 grams(g)/liter (l) to the article 10. This process is preferred when there isa residue that is susceptible to be baked off, as is the case with BTA.In an alternative subprocess, the oxalic acid may be applied without thenecessity of the nitrogen bake. The oxalic acid is useful for removingany copper oxide present on the copper as well as removing any copperparticles which may be present on the non-copper regions of the article10. The oxalic acid may be applied by spraying onto the article 10 orsimply immersing the article 10 in an oxalic acid bath.

In the next step of the process, an aqueous Pd seeding solution isapplied to the article 10. The seeding solution may be applied byspraying or immersion and is usually done at room temperature. Theinventive Pd seeding solution according to the present inventioncomprises the active ingredients of palladium acetate, acetic acid and achloride (i.e., a chloride-containing component) in a water solution.The present inventors have found that a small but effective amount ofchloride leads to a repeatable process wherein there is effectiveseeding with a low increase in resistance of the copper lines (Rs).Conventional Pd seeding solutions comprise palladium chloride orpalladium sulfate. However, such seeding solutions are too aggressivewith respect to the copper, particularly when the copper is used inelectronic applications. If the Pd seeding solution is too aggressive,too much of the copper will be etched, thereby adversely increasing theresistance of the remaining copper. Too, the pH of the Pd seedingsolution is such that undesirable colloidal formation is minimized.

A preferred Pd seeding solution comprises about 0.01 to 0.5 g/lpalladium acetate, 0.25 to 5 volume percent acetic acid and 3 to 10 ppmchloride and most preferably, 0.01 g/l palladium acetate, 0.25 to 1volume percent acetic acid and 3 to 10 ppm chloride. The chloride isactually added as a compound in which the chloride component of thecompound is donated to the seeding reaction. Examples of suitablechloride compounds include but are not limited to hydrochloric acid(HCl), sodium chloride (NaCl), potassium chloride (KCl), ammoniumchloride (NH₄Cl) and palladium chloride (PdCl₂) with hydrochloric acidbeing the most preferred. While PdCl₂ may be used as the chloride, itshould be understood that the Pd donated to the seeding reaction is verysmall and the bulk of the Pd comes from the Pd acetate. PdCl₂, as notedpreviously, is not to be used as the primary supplier of the Pd becausethe seeding is too aggressive and can damage the copper wiring.

The amount of chloride must be tightly controlled in order to have areproducible, and thus manufacturable, process. The amounts of palladiumacetate and acetic acid have a wider range of concentration. If thepalladium acetate is reduced below about 0.01 g/l, Pd seeding becomesdifficult while if the palladium acetate is raised above 0.05 g/l, theresistance of the copper lines is adversely affected in addition to theseed becoming increasingly unstable due to palladium colloid formation.Lowering the acetic acid to the lowest value, 0.25 volume percent andmost preferably 1 volume percent, results in the highest seeding yields.If the acetic acid is reduced below about 0.25 volume percent, then Pdis not dissolved into solution and seeding is adversely affected. Higheracetic acid concentrations beyond 5 volume percent hinder the Pd seedingthereby making it difficult to effectively seed the copper. Therelatively small addition of chloride is critical to the success of thePd seeding solution. The preferred range of the chloride is 3 to 10parts per million (ppm) with the lower end of the range being preferredfor spraying of the Pd seeding solution and the upper end of the rangebeing preferred for immersion of the article 10 in the Pd seedingsolution. It has been found that if the chloride is lowered too much(e.g., below about 2.5 ppm if Pd acetate is about 0.01 g/l and aceticacid is about 0.25 volume percent), there is ineffective seeding whileif the chloride is raised too high (e.g., above 10 ppm if Pd acetate is0.01 g/l and acetic acid is 1 volume percent), the Pd seeding solutionbecomes too aggressive and increases the resistance of the copper.Generally speaking, the pH should be in the range of 2.3 to 3.65, andmost preferably less than 3 for palladium colloid prevention andeffective seeding.

Even with the above components within the claimed range, adjustments maybe need to be made in the concentrations of each of the components withrespect to each other to ensure good seeding with no adverse impact onthe Rs. If the Pd acetate concentration is on the high end of itsconcentration range, the chloride should be on the lower end of itsrange, otherwise there will be an increase in Rs. For acetic acid,higher concentrations of acetic acid hinder effective seeding andrequire higher concentrations of Pd acetate and chloride. As soon as oneof the components (Pd acetate, acetic acid, chloride) is raised orlowered outside of the claimed ranges, it becomes difficult toimpossible to alter the other components to ensure good seeding and goodRs.

The present inventors have further found that notwithstanding thecontrol of the Pd seeding bath as discussed above, colloidal particleswill form. Such colloidal particles are undesirable in that they formunwanted sites where CoWP may form. Accordingly, the present inventorscause the Pd seeding solution to be circulated through a gas filter,preferably with a pore size no larger than 0.006 um, which effectivelyfilters out the vast majority of colloidal particles. Referring to FIG.2, a gas filter having a pore size of 0.02 um or 0.006 um was utilizedduring a Pd seeding step in which Pd sulfate was used as the seedingsolution. The seeded samples were then plated with CoWP and theresulting yield determined as measured by the shorts present. (A shortwould form because CoWP would plate on the colloidal particles, if any,between the copper lines causing a short between the copper lines asmore CoWP was plated.) As can be seen, the yield for the 0.02 um filtersstarted to drop once the CoWP thickness got to around 75 um. On theother hand, the yield for the 0.06 um filter unexpectedly allowed CoWPplating up to 150 um without a drop in yield. For the latter samples,plating was discontinued at 150 um. Even though the graph shows resultsusing a Pd sulfate seeding solution, equivalent results can be expectedusing the Pd acetate seeding solution of the present invention.

During the foregoing seeding step, scattered Pd ions are likely to beadsorbed on non-copper surfaces. The adsorbed Pd ions are undesirable inthat they provide nucleation sites for the electroless deposition ofCoWP at locations other than on the copper and thus are to be avoided.To remove such adsorbed Pd ions, a complication solution is applied(e.g., by spraying or immersion) to the article 10 to remove theadsorbed Pd ions. Preferably, the complexation solution comprises sodiumcitrate or ethylenediamine tetraacetic acid (EDTA) in the amount of 25g/l. The complexation solution is preferably applied at roomtemperature.

The last step of the process according to the present invention is toelectrolessly plate the copper with a plating solution comprisingcobalt, tungsten and phosphorus so as to result in the deposition of aCoWP layer onto the copper. The plating solution may be sprayed on thearticle 10 or the article 10 may be immersed in the plating solution.The plating solution used comprised 6 g/l cobalt sulfate, 25 g/l sodiumcitrate, 30 g/l boric acid, 8 g/l sodium hypophosphate, 2.5 g/l ammoniumtungstate and 0.05 g/l of a surfactant such as L95, available from DowChemical, Midland, Mich. The pH of the plating solution was adjusted to8.95 using sodium hydroxide and the temperature of the plating solutionwas 73° C.

EXAMPLES

The advantages of the invention will become more apparent afterreferring to the following examples.

A series of samples were prepared. Each sample was seeded using anaqueous seeding solution comprising Pd acetate, acetic acid,hydrochloric acid and water but the amount of each of the Pd acetate,acetic acid hydrochloric acid was varied as noted in the table. Some ofthe samples were immersed in the seeding solution while others weresprayed with the seeding solution. Then, each sample was exposed to acomplexation solution to remove adsorbed Pd ions and then electrolesslyplated with a CoWP plating solution. The results are indicated in thetable. Spray Pd Acetic (S) or Sample Acetate Acid HCL Immersion No. g/lvolume % ppm (I) Results 1 0.005 1 3 S Ineffective seeding 2 0.01 0.25 2S Ineffective seeding 3 0.01 0.25 3 S Good seeding, low increase in Rs 40.01 0.25 5 S Good seeding, low increase in Rs 5 0.01 0.25 10 S Goodseeding, increase in Rs 6 0.01 1 3 S Good seeding, low increase in Rs 70.01 1 3 I Good seeding, low increase in Rs 8 0.01 1 5 S Good seeding,low increase in Rs 9 0.01 1 5 I Good seeding; low increase in Rs 10 0.011 10 S Good seeding, increase in Rs 11 0.01 1 10 I Good seeding, low Rs12 0.01 5 10 S Ineffective seeding 13 0.01 5 20 S Increase in Rs 14 0.051 3 S Good seeding 15 0.05 1 5 S Increase in Rs 16 0.07 1 3 S Increasein Rs

The above examples illustrate the effectiveness of the claimed ranges ofthe seeding solution of the present invention as well as theinterdependence of each component of the seeding solution.

In Examples 1 and 2, either the Pd acetate or hydrochloric acid were toolow, resulting in ineffective seeding. Examples 3 to 11 and 14 werewithin the preferred ranges and produced good results. With respect toExamples 5 and 10, while there was good seeding, the hydrochloric acidwas a little high for a spray application, thereby resulting in anincrease in Rs. Were the seeding to be applied by immersion, there wouldstill be good seeding with a lower increase in Rs.

While Example 12 was within the preferred range, there was ineffectiveseeding. This is due to the higher concentration of acetic acid. Thehigher concentration of acetic acid hinders effective seeding andrequires higher concentrations in the Pd acetate and/or hydrochloricacid. However, at much higher concentrations of hydrochloric acid, suchas the 20 ppm shown in Example 13, there is better seeding but a highRs.

Examples 15 and 16 both result in high Rs, although Example 15 is withinthe preferred range. Since the Pd acetate is at the high end of itsconcentration range, the hydrochloric acid should be at the lower end ofits range, at least less than 5 ppm. On the other hand, when the Pdacetate is out of the high end of the preferred range, there is high Rseven for very low concentration of hydrochloric acid as illustrated byExample 16.

It will be apparent to those skilled in the art having regard to thisdisclosure that other modifications of this invention beyond thoseembodiments specifically described here may be made without departingfrom the spirit of the invention. Accordingly, such modifications areconsidered within the scope of the invention as limited solely by theappended claims.

1. A method of electrolessly plating on copper contained in or on asubstrate comprising the steps of: applying to the substrate an aqueousseeding solution of palladium acetate, acetic acid, and chloride so asto form a palladium seed layer on the copper only and not on theremainder of the substrate, applying to the substrate a complexingsolution to remove palladium ions adsorbed on the substrate; andelectrolessly plating the copper with a plating solution comprisingcobalt, tungsten and phosporus so as to deposit a layer of cobalt,tungsten and phosphorus on the palladium seed.
 2. The method of claim 1further comprising the step of precleaning the copper prior to the stepof applying to the substrate a seeding solution.
 3. The method of claim2 wherein the step of precleaning comprises heating the substrate at100° C. in nitrogen followed by applying an oxalic acid solution to thesubstrate.
 4. The method of claim 2 wherein the step of precleaningcomprises applying an oxalic acid solution to the substrate.
 5. Themethod of claim 1 wherein the solution of palladium acetate, aceticacid, and chloride comprises 0.01 g/l palladium acetate, 0.25 to 5volume percent acetic acid and 3 to 10 ppm chloride.
 6. The method ofclaim 5 wherein the chloride is selected from the group consisting ofhydrochloric acid, sodium chloride, potassium chloride, ammoniumchloride and palladium chloride.
 7. The method of claim 5 wherein thechloride is hydrochloric acid.
 8. The method of claim 1 wherein thesolution of palladium acetate, acetic acid, and chloride comprises 0.01g/l palladium acetate, 0.25 to 1 volume percent acetic acid and 3 to 10ppm chloride.
 9. The method of claim 8 wherein the chloride is selectedfrom the group consisting of hydrochloric acid, sodium chloride,potassium chloride, ammonium chloride and palladium chloride.
 10. Themethod of claim 8 wherein the chloride is hydrochloric acid.
 11. Themethod of claim 1 wherein the complexing solution comprises a complexingagent selected from the group consisting of sodium citrate andethylenediamine tetraacetic acid (EDTA).
 12. The method of claim 11wherein the complexing agent is present in the amount of 25 g/l.
 13. Themethod of claim 1 comprising the step of circulating at least theseeding solution through a gas filter to remove unwanted particles. 14.The method of claim 13 wherein the gas filter has an average pore sizeof 0.006 microns.
 15. A method of depositing a seed layer on coppercomprising the step of: applying to the copper an aqueous solution ofpalladium acetate, acetic acid, and a chloride so as to form a palladiumseed layer on the copper only.
 16. The method of claim 15 farthercomprising the step of precleaning the copper prior to the step ofapplying to the copper a seeding solution.
 17. The method of claim 16wherein the step of precleaning comprises heating the copper at 100° C.in nitrogen followed by applying an oxalic acid solution to the copper.18. The method of claim 16 wherein the step of precleaning comprisesapplying an oxalic acid solution to the copper.
 19. The method of claim15 wherein the solution of palladium acetate, acetic acid, and chloridecomprises 0.01 g/l palladium acetate, 0.25 to 5 volume percent aceticacid and 3 to 10 ppm chloride.
 20. The method of claim 19 wherein thechloride is selected from the group consisting of hydrochloric acid,sodium chloride, potassium chloride, ammonium chloride and palladiumchloride.
 21. The method of claim 19 wherein the chloride ishydrochloric acid.
 22. The method of claim 15 wherein the solution ofpalladium acetate, acetic acid, and chloride comprises 0.01 g/lpalladium acetate, 0.25 to 1 volume percent acetic acid and 3 to 10 ppmchloride.
 23. The method of claim 22 wherein the chloride is selectedfrom the group consisting of hydrochloric acid, sodium chloride,potassium chloride, ammonium chloride and palladium chloride.
 24. Themethod of claim 22 wherein the chloride is hydrochloric acid.
 25. Themethod of claim 15 comprising the step of circulating the seedingsolution through a gas filter to remove unwanted particles.
 26. Themethod of claim 25 wherein the gas filter has an average pore size of0.006 microns.
 27. A method of electrolessly plating on copper containedin or on a semiconductor wafer comprising the steps of: providing asemiconductor wafer having copper areas and non-copper areas; applyingto the semiconductor wafer an aqueous solution of palladium acetate,acetic acid, and chloride so as to form a palladium seed layer on thecopper areas only and not on the non-copper areas; applying to thesemiconductor wafer a complexing solution to remove palladium ionsadsorbed on the non-copper areas; and electrolessly plating the copperwith a plating solution comprising cobalt, tungsten and phosporus so asto deposit a layer of cobalt, tungsten and phosphorus on the palladiumseed.
 28. The method of claim 27 further comprising the step ofprecleaning the copper prior to the step of applying to thesemiconductor wafer a seeding solution.
 29. The method of claim 28wherein the step of precleaning comprises heating the semiconductorwafer at 100° C. in nitrogen followed by applying an oxalic acidsolution to the semiconductor wafer.
 30. The method of claim 28 whereinthe step of precleaning comprises applying an oxalic acid solution tothe semiconductor wafer.
 31. The method of claim 27 wherein the solutionof palladium acetate, acetic acid, and chloride comprises 0.01 g/lpalladium acetate, 0.25 to 5 volume percent acetic acid and 3 to 10 ppmchloride.
 32. The method of claim 31 wherein the chloride is selectedfrom the group consisting of hydrochloric acid, sodium chloride,potassium chloride, ammonium chloride and palladium chloride.
 33. Themethod of claim 31 wherein the chloride is hydrochloric acid.
 34. Themethod of claim 27 wherein the solution of palladium acetate, aceticacid, and chloride comprises 0.01 g/l palladium acetate, 0.25 to 1volume percent acetic acid and 3 to 10 ppm chloride.
 35. The method ofclaim 34 wherein the chloride is selected from the group consisting ofhydrochloric acid, sodium chloride, potassium chloride, ammoniumchloride and palladium chloride.
 36. The method of claim 34 wherein thechloride is hydrochloric acid.
 37. The method of claim 27 wherein thecomplexing solution comprises a complexing agent selected from the groupconsisting of sodium citrate and ethylenediamine tetraacetic acid(EDTA).
 38. The method of claim 37 wherein the complexing agent ispresent in the amount of 25 g/l.
 39. The method of claim 27 comprisingthe step of circulating at least the seeding solution through a gasfilter to remove unwanted particles.
 40. The method of claim 39 whereinthe gas filter has an average pore size of 0.006 microns.
 41. The methodof claim 27 wherein the copper comprises copper interconnect wiring. 42.A seeding solution for depositing a palladium seed on copper comprisingan aqueous solution of palladium acetate, acetate and chloride.
 43. Theseeding solution of claim 42 wherein the aqueous solution of palladiumacetate, acetic acid, and chloride comprises 0.01 g/l palladium acetate,0.25 to 5 volume percent acetic acid and 3 to 10 ppm chloride.
 44. Theseeding solution of claim 42 wherein the aqueous solution of palladiumacetate, acetic acid, and chloride comprises 0.01 g/l palladium acetate,0.25 to 1 volume percent acetic acid and 3 to 10 ppm chloride.